On Aérial Navigation. 327 
he had the disadvantage of carrying the weight of a man upon 
his back. If therefore the energies of birds be taken at double 
those of quadrupeds in this statement, more than an ample al- 
lowance is made in their favour. This power in birds is chiefly 
employed in the waftage necessary for their support, and a smaller 
portion of it is applied to overcome the direct resistance of their 
body: but in the case of the balloon the supporting power is al- 
ready obtained, and the whole energies of the first mover will 
be directed towards overcoming the resistance of the prow ouly, 
which is in no greater proportion to the weight of the whole 
apparatus than that of the bird to its weight. 
Upon estimating the probable weight even of steam-engines 
upon a large scale, it appears that 160 pounds per horse power 
is an ample allowance with its load of coal and water for one 
hour *; and as the water is a considerable part of the whole, and 
can be recovered again for the use of the engine by permitting 
the steam to pass within the double coats of the balloon, and to 
be thus exposed to so extensive a cooling surface, it is probable 
that 200 pounds per horse power will be more than sufficient 
for working twelve hours without any further supply of water or 
fuel—with a velocity of 20 miles per hour in calm air, this 
length of time would imply a stage of 240 miles. The steam- 
horse power raising 550 pounds one foot high per second, is 
considered by engineers as exceeding the average power of the 
largest dray-horses one-fourth. Upon weighing one of these 
animals of about the middle size, I found it to be fourteen hundred 
weight or 1568 pounds; and I am informed Some of the largest 
of these horses have weighed a ton.—But if we take the smaller 
weight as approaching the average, we must increase it one- 
fourth part to make an animal equal in power to the steam- 
horse: hence the weight of the steam-horse will be as 200 
pounds to 1950 pounds when compared to that of the living 
animal. And to follow the argument I have been using, if the 
* Estimate of the Weight of an Expansive Steam-engine of 100 Horses Power. 
Weight of a cylinder 2 ft. 4 inch. diameter by 4 ft. 7 inch. in length ) sie 
one inch thick ~— = - - mw de - - - ah ae 
400 feet surface of tubulated boiler at ten pounds per foot - 4000 
Connecting parts, piston, &c. say - - ~ - - 2000 
Water for an hour at 30 pounds per horse’s power - = 8000 
Coal for ditto at five pounds per ditto, being more than sufli-) 500 
cient in Mr. Woolf's engines - ~ - - . 
Weight of fuel constantly occupying the fire-place, say - - 1500 
Weight of water occupying the boiler - - - 3000 
15210 
The pressure is estimated at 20 pounds per square inch, and the stroke 
4 ft. 7 inch, each second, 
i. X 4 weight. 
